1. Field of the Invention
The present invention relates to visual display terminals associated with memory banks of a computer system. More particularly, this invention relates to control means for visual display terminals which perform the editing of any of the characters displayed on the visual panel of the display terminal which are representative of data characters stored in the memory.
2. Description of the Prior Art
In numerous computer systems it is desirable to visually examine the content of memory in a printed page or tabular format having columns and rows of alpha numeric characters. It is further desirable to be able to change or edit single characters, words or lines of alpha numeric characters and to store the edited printed page format back into the display memory, and from there back into the mass memory of the computer system.
Visual display terminals such as those shown in U.S. Pat. No. 3,466,645 are manufactured by the Sperry Rand Corporation and are provided with keyboard function keys and data entry keys which permit edit operation such as a delete or insert operation. The shift-edit operation in such devices permits the data to roll or be displayed in a scroll format fashion. Heretofore, the preferred manner of implementing the shift-edit function was to employ very large shift registers which would permit a display in scroll fashion. Large multiple output shift registers used in the prior art are relatively slow, expensive and are not overly tolerant of ionizing radiation.
Heretofore, numerous prior art visual display terminals employed numerous discrete components and employed procedures which operated to lock out other functional uses of the visual display terminal.
Semiconductor manufacturers have suggested that microprocessors may be employed as a substitute for hard wired logic to provide a sequence of programs which would simplify circuitry required to perform logical functions such as edit functions. Special design microprocessors are relatively expensive and are very slow when compared to hard wired integrated circuit gating logic.
Heretofore, the control circuitry in a visual display terminal which was employed to accomplish memory shift and edit functions was expensive, complex, relatively slow and so designed as to prevent the useful operation of the visual display terminal for other useful work. In those visual display panels which did not lock out the operation of other functions, the edit functions were so time consuming as to preempt any attempt to accomplish other useful work.